1. Field of the Invention
The present invention generally relates to method and system for measuring the S/N ratio of a television (TV) signal or a video signal. The invention also relates to a system for executing a process according to a result of measurement of the S/N ratio.
2. Description of Related Art
Among techniques for measuring the S/N ratio of a TV signal transmitted via radio wave or a wire, there is for example is a technique configured such that a detection output of a video signal in a received TV signal is integrated and its integration output level is checked, It is a general way to fundamentally detect an average noise level or an information signal level in a demodulation output of the video signal.
In the measurement based on the average level detection, it cannot be, however, always said that the S/N ratio can be detected accurately in accordance with a fluctuation in an actual S/N ratio and the fluctuation in the S/N ratio can be captured at a high response speed. In many cases, there is a tendency such that a circuit for the measurement is complicated and the cost increases.
When performing a process which needs to be performed precisely in accordance with the fluctuation of the S/N ratio and at a high response speed, for example, a diversity process as an anti-multipath method in a television receiving system, therefore, even if a conventional S/N ratio measuring technique is applied, the system cannot be successfully adapted to a reception environment or a large-scale circuit for successful adaptation is necessary.
More specifically, when detecting the existence of noises, amplitude components of the noises are usually extracted as amplitude information by a method of detection (rectification and smoothing) or the like. If a method of limiting a frequency component by a high pass filter or the like is included in the detection process, frequency information will be also included in addition to the amplitude information. In the S/N ratio measurement, to be exact, the level (amplitude information) of noises when a signal S is at a constant level has to be extracted.
When obtaining information according to the S/N ratio in order to realize the diversity method, if it is intended to obtain the level information of the noises by methods of rectification and smoothing or the like, it is difficult to manage parameters regarding level information such as gain, threshold value, and the like in the rectifying and smoothing circuit. In other words, the circuit has to be strictly set with respect to a variation in component elements, temperature characteristics, and the like of the circuit.
Consequently, there arise cases where the circuit is enlarged in scale and complicated and the adjustment is unavoidable on a product. In addition, the circuit also has an aspect such that there are many disadvantages in mounting of parts onto a circuit board due to the necessity of a smoothing capacitor and the like.
The invention is, therefore, made in view of the foregoing drawbacks and it is an object of the invention to provide a method of measuring an S/N ratio of a video signal, in which it is suitable for realization of an IC and a fluctuation in an S/N ratio of a television signal or a video signal can be accurately detected at a high response speed while suppressing a total cost and to provide a system based on the method.
According to the invention, there is provided a method of measuring an S/N ratio of a composite video signal, wherein the composite video signal is received, a noise density in a predetermined period of the composite video signal is detected, and the SIN ratio of the composite video signal is recognized based on the detected noise density.
According to the invention, there is provided another method of measuring an S/N ratio of a composite video signal, wherein the composite video signal is received, noises occurring in a predetermined period of the composite video signal are counted, and the S/N ratio of the composite video signal is recognized based on a count value obtained by the counting operation.
In each of the methods, the predetermined period can be set within a generating period of a vertical sync signal.
According to the invention, there is provided a system for measuring an S/N ratio of a composite video signal, comprising: demodulating means for demodulating the composite video signal from a reception signal; and counting means for counting noises occurring in a predetermined period of the composite video signal, wherein the S/N ratio of the composite video signal is recognized based on a count value obtained by the counting means.
In the system, the predetermined period can be set within a generating period of the vertical sync signal.
According to the invention, there is provided another system for measuring an S/N ratio of a composite video signal and executing a process according to a measurement result, comprising: S/N ratio measuring means for receiving the composite video signal, counting noises occurring in a predetermined period of the composite video signal, and recognizing the S/N ratio of the composite video signal based on a count value obtained by the counting operation; and control means for executing a control according to the S/N ratio obtained by the S/N ratio measuring means.
According to the invention, there is provided further another system for measuring an S/N ratio of a composite video signal and executing a diversity process according to a measurement result, comprising: S/N ratio measuring means for receiving the composite video signal, counting noises occurring in a predetermined period of the composite video signal, and recognizing the S/N ratio of the composite video signal based on a count value obtained by the counting operation; and control means for executing a diversity process in accordance with the S/N ratio obtained by the S/N ratio measuring means.
The still another system further comprises switching means for selectively switching reception of outputs from a plurality of receiving antennas, wherein the control means can generate an instruction for switching the selection of the receiving antenna in accordance with the recognized S/N ratio to the switching means.